Food allergy affects up to 6% of the pediatric population, and up to 3.5% of adults in the United States. Strict allergen avoidance is currently the only approach to the management of food allergy. We have developed a novel immunotherapeutic agent, EMP-123, for the treatment of peanut allergy. We have previously shown that EMP-123 abolishes anaphylaxis in response to oral peanut challenge in peanut-allergic mice. The studies outlined in this application are designed to determine the mechanisms responsible for EMP-123- mediated desensitization to peanut in sensitized mice. We hypothesize that EMP-123 inhibits anaphylaxis by two mechanisms: the induction of antigen-specific regulatory T cells and by modulation of intestinal barrier function. We will first examine innate immune mechanisms of response to EMP-123. We will determine what cells take up EMP-123 encoded antigen, what the impact of the bacterial components are on the phenotype of antigen-bearing cells, and the outcome of interaction between antigen-bearing cells and naive T cells. We will determine the role of host toll-like receptors in sensitization to peanut, and desensitization using EMP- 123. The hypothesis that EMP-123 induces T regulatory cells will be directly tested using cell transfer studies. These studies are designed to comprehensively determine immune mechanisms of desensitization to peanut using EMP-123. Another component of the innate immune system is epithelial barrier function, and we hypothesize that EMP-123 treatment results in normalization of barrier function by interfering with sensitization-induced alterations in antigen uptake. We will determine cellular mechanisms of antigen uptake and the role of IgE and CD23-mediated antigen uptake in the context of normal health, peanut sensitization, and desensitization with EMP-123. The results from these studies will identify potential biomarkers tracking the progress of desensitization in humans and will potentially help us to refine EMP-123 for more specific and effective treatment of peanut allergy in humans.